This invention relates to gauges for determining the fineness of particles dispersed in a liquid medium. The invention has particular application in the manufacture of paints for determining the fineness of pigment particles dispersed in a resin base after grinding.
One known gauge for determining the fineness of pigment particles in paints is the Heckmann gauge. This comprises an elongated metal block with a longitudinal groove in its upper surface, the depth of the groove gradually decreasing from one end to the other. In use of this gauge a load of paint is placed at the deep end of the groove and drawn along it by a spreader blade whose knife edge is in contact with the upper surface of the metal block. In this way the paint will be spread along the groove until the depth of the groove is less than the diameter of the pigment particles. The paint will then be scraped along the bottom of the groove by the spreader leaving, so to speak, a cut-off position in the groove. The upper surface of the block is marked with a scale along its length indicating for example the depth of the groove at various positions along it so that the cut-off position can be read off this scale and from this reading the pigment particle size can be interpreted.
One disadvantage of this known gauge is that the cut-off position can not be easily determined, because it is in most cases formed by a jagged line across the groove. Another disadvantage is that with solvent based paints some of the solvent evaporates during the test and so the cut-off position tends to creep back.
The object of the invention is to overcome the aforesaid disadvantages.